Red-luminescent substance and method of preparation thereof



3,014,875 RED-LUMDJESCENT SUBSTANCE AND METHGD F PREPARATION THEREDF Wilhelmus Polycarpus de Great and J an Lourens Ouweltjes, Eindhoven, Netheriands, assignors to North American Philips Company, Inc, New York, N .Y., a corporation of Delaware No Drawing. Filed Dec. 23, 1958, Ser. No. 782,384

Claims priority, application Netherlands .lan. 2, 1958 4 Claims. ((32. 252301.4)

This invention relates to a source of radiation comprising the combination of a high-pressure mercury vapor discharge tube and a luminescent screen contaim'ng a red-luminescent substance, the emission of which upon excitation by the ultraviolet radiation lies substantially wholly above 600 mg. The invention also relates to a luminescent substance having this red emission and to a method of manufacturing said substance.

British patent specification No. 701,033 discloses a source of rays of the above-mentioned kind, in which the radiation of the red-luminescent substance serves to supplement the red emission which is unduly weak in the radiation of such a discharge tube. This substance is a compound of magnesium oxide, magnesium fluoride and germanium oxide, activated with quadrivalent manganese and obtained by heating and in which per molecule of germanium oxide, the sum of the amount of magnesium oxide and magnesium fluoride in molecules lies between 2 and 4.6.

According to the indications of the said British patent specification, many hundreds of sources of rays have been manufactured which proved quite satisfactory in practice. However, a great disadvantage of the red luminescent substances employed is the high cost of germanium, since germanium is a rare element and can be manufactured from the minerals with difiiculty only, more particularly with the degree of purity necessary for the manufacture of luminescent substances.

Substances of the same good luminescent properties have been sought for use in sources of rays of the abovedescribed kind which contain almost exclusively elements which occur in large quantities and from which the required compounds may be obtained at low cost. It has been found that few luminescent substances exist which luminesce so intensely in the desired region and at the same time exhibit the same low temperature dependency of the emission as the above-mentionedgermanates, since the latter, even at temperatures of 250 C., retain an emission the quantum efificiency of which is not lower than about 80% of that at room temperature. This is of great importance since the luminescent substances are preferably provided in close proximity to the discharge tubes which have a high temperature.

Experiments having led to the present invention revealed that a portion of the germanium oxide may be substituted by the combination of silicon dioxide and one or both oxides of titanium and tin. The good properties of the non-substituted germanate are then completely retained, whilst in certain cases even additional advantages are obtained.

A source of rays according to the invention comprises the combination of a high-pressure mercury vapor discharge tube and a luminescent screen containing a redluminescent substance, the emission of which upon excitation by the ultraviolet radiation lies almost completely above 600 m and it is characterized in that the red luminescent substance has a molecular composition which satisfies the formula a.MgOb.MgF .c.GeO .p.SiO .q.TiO .r.SnO .z.MnO

wherein a has a value comprised between 3.0 and 3.9

a+b=4 +p+ q+r= 1 10+ q-l-r has a. value comprised between 0.10 and 0.40 70 has a value comprised between 0.01 and 0.36 g has a. value comprised between 0 and 0.36 r has a. value comprised between 0 and 0.36

P 9+ 2 has a value comprised between 0.005 and 0.020

As appears from the above-mentioned formula and conditions, a substance according to the invention differs from the above-described substances only in that a portion of the germanium dioxide is substituted by silicon dioxide in combination with one or both oxides of tin and titanium. Since the compounds of silicon, titanium and tin are considerably cheaper than compounds of germanium, it is advantageous to substitute the germanium dioxide by the said three oxides in as large a pro portion as possible. However, it has been found that a limit is set to this substitution, since the light output declines too much if the percentage of silicon dioxide, titanium oxide and tin oxide is unduly high. A small decline in the light output is permissible because of the important saving in cost. However, since with determined substitution percentages a higher light output is obtained, as will be explained more fully hereinafter with has a value comprised between 0.1 and 9.0

reference to a few tables, these percentages are preferably chosen,

It has been found that substitution of so large a portion of the germanium oxide that a reasonable economy is obtained, by only one of the oxides of silicon, titanium or tin, or by tin oxide and titanium oxide always leads to a considerably lower light output. A substance for use in a source of rays according to the invention thus always contains silicon dioxide and at least one of the two other oxides.

The manufacture of the red-luminescent substance of the above-mentioned formula is substantially the same as the manufacture of known germanates. By way of illustration three examples now follow hereinafter.

Example I A mixture is manufactured from 124 gs. of MgO 56 gs. of MgF 8.0 gs. of TiO 84 gs. of GeO 0.7 g. of Mn0 6.0 gs. of SiO:,,

Example II A mixture is manufactured from gs. of MgO 31 gs. of MgF 15.1 gs. of smo 74 gs. of GeO 0.9 g. of- MnO- This mixture is heated in air at a temperature of 1000 C; for 8 hours. The reaction product obtained isv ground and sieved and is then ready for use.

Example 111 A mixture is manufactured from 140 gs. of M o 31 gs. of MgF 84 gs. of GeO 12.0 gs. of SiO 8.4 gs. of SiO 2.4 gs. of TiO 4.5 gs. of SnO 1.3 gs. of MnO;

This mixture is heated in air at a temperature of 1200 C. for 3 hours. After heating, the reaction product is ground and, if necessary, sieved and is then ready to be provided on the luminescent screen of the source of rays according to the invention.

4 In order to give an impression of the economy which may be obtained by using the invention, it is mentioned that each source of rays comprising a high-pressure mercury vapor discharge tube of usual size and surrounded I I 5 by a bulb of approximately spherical shape, having a The table now following shows the light output upon radius of 5 cms. requires 2 guns. of germanate. This excitation by a radiation of 253,7 f a large mb r germanate contains .8 g. of germanium oxide if no use is of compounds with the formula made of the invention. if instead of 1 mol. of germanium M V oxide, 0.2 tool. is substituted by a mixture of silicon zz-lz l- 9 2 10 dioxide and titanium dioxide in a ratio 1:1, the cost of 1 coating a bulb is decreased by about 8%. With the acas g non'subsmmed the hght tual prices of germanium dioxide, this yields for 1000 output of which is assumed to be 100.

I bulbs an economy of about 50 guilders.

n this table, the first horizontal row indicates the ratio Geo /Si0 d th 1 t 1 1 What 1s claimed 15. the g an 6 as ve lea indicates 1. A red-luminescent substance, the emission of which i o 1 1 2 upon excitation by ultra violet radiation lies substantially Wholly above 600 me, said red-luminescent sub- Geofl 0.8 0.7 0.6 siot stance having a molecular composition which satisfies Oz-i-TiOz 0'2 03 M the formula:

-a.MgO.b.MgF .c.GeO .p.Si0 .q.TiO .r.SnO .z.MnO 97 so 83 3:7 1 g g5 89 4 wherein 101 as 93 634 a has a value between 3.0 and 3.9 a a a s as 89 so 05 +q+r=1 p-l-q-l-r has a value between 0.10 and 0.40 p has a value between 0.01 and 0.36 The table now following indicates in the same manner 0 has a value between 0 and 0.36 as above in the first table, the light output, but with the T h a value between 0 and 3 use of tin oxide instead of titanium oxide. gr has a Value between 01 and 9.0 Geog 0.5 0,7 on $103 .2 has a value between 0.005 and 0.020 S102+S1102 0.2 0,3 0,4 $1102 2. The red-luminescent substance of claim 1 which satisfies the formula: 3?, 33 3g 2;; a.MgO.b.MgF .c.GeO .p.SiO .q.TiO .r.SnO .zMnO 9s 93 so 5:5 a a a 94 92 75 822 a has a value between 3.0 and 3.9 93 84 75 9:1 40 =4 C+P+Q+T=1 l b t 010 c1040 In order to give an impression of the light outputs of p+q+r has Va e ween 10 has a value between 0.03 and 0. substances contalmng, n addition to sllicon dioxide, both g has a value between 0 and 028 titanium oxide and tin oxide, compounds have been T has a Value between 0 d 0,23 manufactured with 0.8 mol. of Ge0 and 0.14 mol. of p Si0 and a constant sum, viz. 0.06 mol. of TiO and has a value between 0.4 and 2.5 SnO The table now following indicates the light out- 9 5 d 0 020 puts of these substances as compared with the light output 2 has a Value between p of a substance with exclusively 1 mol. of 6e0 which is 3. A method of manufacturing the luminescent subassumed to be 100. stance of claim 1 wherein a mixture of magnesium ox- TABLE Light output 3.5 MgO 0.5 hIgFz 0.01 M110, 0 8 GeO: 0.14 s10, 0.04 T102 0.02 S1102 100 3.5 MgO 0.5 MgFa 0.01 MnO: 0 8 G00: 0.14 s10: 0.03 Ito: 0.03 SE02 104 3.5 MgO 0.5 MgF: 0.01 MnO: 0 8 GeOz 0.14 Bio: 0.02 T10: 0.04 SD02 90 As may appear from the foregoing tables, the light output obtained is not always constant, but there is a region in which the light output is maximum. The red-luminescent substance is therefore preferably chosen, so that in the above formula q-l- I .2 has a value comprised between 0.005 and 0.020

has a value comprised between 0.4 and 2.5

References Cited in the file of this patent UNITED STATES PATENTS 2,457,054 Leverenz Dec. 21, 1948 2,697,076 Anderson Dec. 14, 1954 FOREIGN PATENTS 1,139,056

France June 25, 1957 

1. A RED-LUMINESCENT SUBSTANCE, THE EMISSION OF WHICH UPON EXCITATION BY ULTRA VIOLET RADIATION LIES SUBSTANTIALLY WHOLLY ABOVE 600 MA, SAID RED-LUMINESCENT SUBSTANCE HAVING A MOLCEULAR COMPOSITION WHICH SATISFIES THE FORMULA: 